Mediastinal seminoma with florid follicular lymphoid hyperplasia: a clinicopathological and immunohistochemical study of six cases.

Seminomas are unusual primary tumors of the anterior mediastinum. Morphologically, they are indistinguishable from their testicular counterparts; however, in the mediastinum, the occurrence of secondary changes such as cyst formation is not uncommon. We now describe six cases associated with florid follicular hyperplasia. The patients were male with an age range from 24 to 31 years. Clinically, symptoms included cough, dyspnea, and chest pain. Anterior mediastinal masses were detected on imaging and all patients underwent thymectomy. Macroscopically, all tumors had a fleshy, lobulated cut surface. Histologically, the tumors were composed of round to polygonal cells with indistinct cell borders, clear cytoplasm, and prominent nucleoli. Striking follicular hyperplasia was evident in all cases to a degree whereby the tumor component was nearly obscured. Immunohistochemical studies demonstrated that the germinal centers were largely composed of B lymphocytes, and T cells were the predominant component of the interfollicular areas. Scattered Langerhans cells were noted in between tumor cells, and dendritic cells were seen in the mantle zones. All cases failed to show light chain restriction. Follow-up showed that five patients were alive and well 1-5 years after diagnosis, while one was lost to follow-up. Thymic seminomas can be associated with striking lymphoid follicular hyperplasia, likely as a response to specific tumor antigens. Familiarity with this variant of thymic seminoma is important in order not to misdiagnose these cases for reactive conditions or other tumors such as lymphoproliferative neoplasms which may require a different treatment approach.